Many types of material handling implements include hydraulic drive systems which are adapted for directional and speed control from a single pivoting control lever. Frequently, steering of such implements can be effected by transverse movement of the single control lever, with such arrangements sometimes referred to as "mono stick" control assemblies. As will be recognized, such control arrangements are very easily used since an operator need only manipulate a single control lever to control forward and reverse travel speed, as well as steering of the implement.
For the operation of some implements, it is desirable to maintain a constant and relatively low speed of movement. For example, the use of a trencher attachment on an implement usually requires that the operator of the implement maintain a generally constant speed for the implement as the trencher operates in the soil. Without careful control of the implement's speed, the trencher attachment cannot work at optimum efficiency.
Frequently, control levers as described above are configured to self-center, i.e., return to a neutral position when released by the operator. This self-centering action can be provided by centering springs operatively associated with the control lever, or may be a result of hydraulic pressure feedback, such as is the case when the lever operates a variable displacement hydraulic pump. Because it would be fatiguing for an operator to maintain a constant rate of speed for the implement by continued manipulation of the control lever, it is desirable to provide an override or control locking arrangement which permits the lever to be maintained in a constant position
Commonly assigned U.S. Pat. No. 4,321,980, to Nissen, illustrates a so-called mono stick assembly with adjustable "creep" control, with the term "creep" referring to the capability of the assembly of being set for controlling the associated implement for constant, relatively low speed movement. While the control assembly of this patent desirably permits the operator to maintain a constant speed without continued manipulation of its control lever, the arrangement illustrated is somewhat complex and can be inconvenient to adjust and maintain.
Therefore, it is desirable to provide a control assembly which permits normal operation of an associated hydraulic pump or like device, and which also facilitates "fine" control of the pump. Preferably, such an arrangement should be readily fabricated and easy to operate, and should also preferably be adapted to permit control of a related function, such as implement steering.